ChatGPT Custom Instructions: How to Set Them Up (2026)
ChatGPT custom instructions are standing preferences that ChatGPT applies to every new chat, so you never have to repeat yourself. You set them in Settings under Personalization, then type how you want replies to sound and what ChatGPT should know about you. Free and Go plans allow 1,500 characters, and paid plans allow 5,000.
What are ChatGPT custom instructions?
ChatGPT custom instructions are a short set of notes that ChatGPT reads before it answers anything. Instead of starting each chat with "keep it brief" or "I am a primary school teacher", you write it once and it applies from then on. OpenAI says the instructions apply immediately to all chats, including ones you already have open.
They are useful because ChatGPT otherwise knows nothing about you. A single paragraph about your job, your tone and your preferred format can make every answer feel more relevant.
How do you set up ChatGPT custom instructions?
The steps are short. OpenAI lists the same route for web and desktop, with a slightly different menu name on phones.
On the web or desktop app
Click your profile picture and open Settings.
Choose Personalization.
Make sure Enable customization is switched on.
Open Custom instructions and type your notes.
Save. The change applies to your next message.
On iPhone or Android
Open Settings in the ChatGPT app.
Tap Customize ChatGPT.
Check that Enable customization is on.
Enter your notes in the Custom instructions field and save.
If you cannot find the option, the menu wording may have moved. The OpenAI Help Center page linked at the bottom of this guide is kept up to date.
How many characters can you use?
Free and Go users can save up to 1,500 characters. Plus, Pro, Business, Enterprise and Education users can save up to 5,000, according to OpenAI. That is roughly 250 words on a free plan and about 800 on a paid one, so write tightly. If you are unsure what each plan includes, see our guide to ChatGPT plans.
What should you write in your custom instructions?
Good instructions are specific and short. Cover three things: who you are, how you want answers, and what to avoid.
Who you are: "I run a small bakery in Leeds and write my own social posts."
Tone: "Friendly, plain British English, no jargon."
Format: "Start with the answer, then give three bullet points at most."
Limits: "If you are not sure, say so rather than guessing."
Can you see a worked example?
Here is a prompt you can copy and adapt. Replace the details in brackets with your own.
About me: I am a [job] working in [industry]. I am comfortable with basics but not technical detail.
How to reply: Use British English. Answer first, explain after. Keep replies under 200 words unless I ask for more. Use numbered steps for any process.
Avoid: Marketing language, long introductions and made up facts. Say "I am not certain" when that is true.
Test it by asking a question you asked before. If the style has not changed, check that Enable customization is on and that your notes saved.
What mistakes should you avoid?
Writing a huge essay. Long lists of rules get diluted, so keep to your top five.
Adding private details. OpenAI notes that instructions can inform model improvement unless you opt out, and plug-in developers may see relevant parts if you use third party plug-ins.
Contradicting yourself, for example asking for short and very detailed answers together.
Forgetting that a chat can still override them. If you give a direct instruction in a message, it usually wins for that conversation.
For a fuller picture of what happens to your information, read our plain English ChatGPT privacy guide.
How are custom instructions different from memory and projects?
Custom instructions are fixed notes that you write and control. Memory is information ChatGPT picks up from your chats over time. Projects group related chats and files under one workspace with their own instructions. Use custom instructions for habits that never change, and projects for work with a specific goal. Learn more in our guide to ChatGPT Projects.
Frequently asked questions
Are ChatGPT custom instructions free?
Yes. OpenAI says custom instructions are available on all plans, on web, desktop, iOS and Android. Free users just have a lower character limit of 1,500.
Do custom instructions apply to old chats?
The setting applies immediately across all chats, including existing conversations. However, answers already given do not change. Only new replies follow the updated notes.
Can I turn custom instructions off without deleting them?
Yes. Open Personalization and switch Enable customization off. Your text can stay saved, or you can clear it if you want a clean start.
Is there an API for custom instructions?
No. OpenAI says developers should use system messages in the Chat Completions API for a similar effect.
Are my custom instructions deleted with my account?
Yes. OpenAI says instructions tied to your account are deleted within 30 days when you delete the account. They are also included in your data export.
Why is ChatGPT ignoring my custom instructions?
Check that customisation is switched on and that your notes saved. Then simplify them, because long or conflicting rules are easier for the model to miss.
Key Takeaways
Custom instructions apply your preferences to every chat automatically.
Find them in Settings, Personalization on web, or Customize ChatGPT on mobile.
The limit is 1,500 characters on Free and Go and 5,000 on paid plans.
Keep them short, specific and free of private details.
You can switch them off or edit them at any time.
Bottom line
A few minutes writing ChatGPT custom instructions saves you repeating yourself for months. Start small, test one change at a time, and refine as you learn what works. Explore more ChatGPT guides on whatischatgpt.co.uk.
